Tap changer having cylinder to cylinder contact



1956 s. s. STENERSEN 2,760,017

TAP CHANGER HAVING CYLINDER TO CYLINDER CONTACT Filed May l0, l9 54 2 Sheets-$heet 1 fxQwumutorL 11m g bcmewmm X2 WW Aug. 21, 1956 s. s. STENERSEN 2,760,017

TAP CHANGER HAVING CYLINDER TO CYLINDER CONTACT Filed May 10, 1954 2 Sheets-Sheet 2 v I awn/W004 km h fikwmopm mom United States Patent TAP CHANGER HAVDJ G CYLINDER TO CYLINDER CONTACT Sten S. Stenersen, Milwaukee, Wis, assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application May 10, 1954, Serial No. 428,414 6 Claims. (Cl. 200-11) This invention relates in general to electrical switches in which a movable contact member cooperates with another contact member to make or break an electrical circuit, and is directed particularly to the shapes of the contacting surfaces of the contact members.

Various switches disclosed in the prior art have their contacting surfaces disposed so that during a switching operation a wiping action occurs on the contacting surfaces. This wiping action is desirable and sometimes necessary in cases where the contacting surfaces are apt to become corroded or oxidized between switching operations.

This action is usually obtained by biasing one of the contact members toward the other member and moving one contact member in a plane with respect to the other contact member. While this action insures good contact between the members it increases the wear on the contacting surfaces and limits the type of contact engagement that may be established between the two contacting surfaces to what is referred to as point contact. Two surfaces, by definition, are in point contact when they are in engagement at substantially only one point. Line contact or plane contact has been found impractical for switches with a wiping action because of the difl'iculty of maintaining alignment between the two contacting surfaces as one moves with respect to the other. For this reason, switches utilizing a wiping action usually disposed the contact members so that the contacting surfaces are in point contact engagement. The shapes of the contacting surfaces utilized in the prior art switches all have the disadvantage that one contacting surface tends to wear quite fast. This is because the point of contact viewed with respect to one contacting surface always remains stationary. Stated in other words, as the two contacting surfaces move relative to each other, the point of contact viewed on one surface remains stationary, while Viewed on the other surface the point of contact moves in a predetermined path. The result is that the surface on which the point of contact remains stationary wears quite fast and must be replaced at frequent intervals. This usually happens for example where one contact surface is shaped in the form of a sphere and the other is in t e form of a plane.

In order to increase the wearing ability of the contacting surfaces it is proposed according to the present invention to shape both contacting surfaces so that they may be disposed in point contact engagement and arrange the contact members so that as one member is moved with respect to the other, the point of contact on each contacting surface moves simultaneously on each surface in a predetermined path. The prescnt invention thus maintains the advantages of self-alignment of the contacts and over comes the disadvantages of excessive wear.

It is therefore an object of the present invention to decrease the wearing of the contacting surfaces of a switch.

Another object of the present invention is to provide an improved electrical switch utilizing contact Wiping action, the contacting surfaces of the switch being shaped 2 so that the point of contact on each surface moves simultane'o'usly on each surface.

Objects and advantages other than those mentioned above will be apparent to those skilled in the art from the following description when read in connection with the drawings in which:

Fig. l is a partial isometric view of two contact members embodying the present invention;

Fig. 2 is a plan view of two right cylinders which illustrates the principle of operation involved in the present invention;

Fig. 3 is a partial plan view of a dial switch assembly embodying the present invention; and

Fig. 4 is a view in section of the dial switch shown in Fig. 3 taken along the line IV IV.

Referring to Fig. 1 there is illustrated therein a portion of a switch assembly comprising a first contact member 11 and a second contact member '12. The upper portion of contact member 11 defines a contacting surface 13 which contains a contact line 14. A portion of second contact member 12 defines a contacting surface 16 which contains a second contact line represented by dotted line 17. Contact members 11 and 12 are disposed so that contact lines 14 and 17 intersect causing contacting surface to be in engagement with contacting surface 16 at substantially only one point referred to by reference character A. Contact lines 14 and 17 therefore define a plane which contains the point of contact A of contacting surfaces 13 and 16.

Suitable means is provided for biasing one of the contact members toward the other contact member in order to maintain the contacting surfaces in point contact engagement when one member is moved relative to the other. This biasing means may as shown comprise a cantilever type spring element 18 which has one end 19 fixedly attached to contact member 12 in any suitable manner. In this instance end 19 is fixedly attached to contact member 12 by means of rivet 20. Rivet 20 may be disposed so that its axis would intersect contact line 17 on contacting surface 16 eliminating any tendency of spring 18 to twist about its lengthwise axis, or it may, as shown in Fig. 1, be spaced laterally from contact line 17. The other end of spring element 18 which is not shown in Fig; 1 may be disposed in any suitable manner to cause element 13 to function as a cantilever type spring.

The portion of the switch assembly shown in Fig. 1 may be provided with any suitable means known in the art for causing relative movement between contact members 11 and 12 on an arc in the plane defined by contact lines 14 and 17. This latter type movement may be readily accomplished by having one of the contact members, for example member 11, stationary and rotating contact member 12 on an are having its center spaced laterally from the intersection of contact lines 14 and 17. Moving one contact member in an arc with respect to the other contact member causes the point of contact A to move simultaneously along the contact lines 14 and 17 of contact surfaces 13 and 16, respectively.

This simultaneous movement of the point of contact A along the respective contact lines of contact surfaces 13 and 16 may be readily seen by referring to Fig. 2 which is a plan view of two right cylinders 23 and 24 disposed so that their cylindrical surfaces are in engagement at substantially only one point A. Cylinder 23 has a contact line 26 and cylinder 24 has a contact line 27 which as shown intersect at point A. Cylinder 24 is adapted to be moved on an are 28 of a circle disposed in the plane containing contact lines 26 and 27. These conditions are representative of the conditions shown in Fig. 1. As cylinder 24 is moved clockwise as shown in Fig. 2 from position 1, point A, the point of actual engagement of the two cylinders, moves to the right along contact line 26 on cylinder 23 and simultaneously moves radially inward on contact line 27 until the contact lines 26, 27 are normal to each other, as represented by position 2. As cylinder 24 continues its movement 011 the arc 28, point A continues moving to the right along contact line 26 but moves radially outward on contact line 27 of cylinder 24.

Referring again to Fig. 1 it will be seen that movement of the contact members 11 and 12 in a manner similar to that described with relation to Fig. 2, decreases the wear on contacting surfaces 13 and 16 since the point of contact moves on both surfaces. The advantage of point contact engagement is still maintained.

Figs. 3 and 4 are views of a dial switch assembly having contact members embodying the present invention. The switch assembly shown in these figures comprises a mounting panel 30, a shaft 31 which extends through panel and in this instance is suitably journaled therein, a plurality of stationary contact members 32 which are circumferentially spaced on the arc 33 of a circle having its center on the axis of rotation of shaft 31, and a pair of movable contact members 34, and 35, each of which is operable to interconnect any two adjacent stationary contact members 32. The stationary contact members 32 are similar to contact member 11 of Fig. 1 and only one will be described. Contact member 32, shown in section in Fig. 4, defines a pair of cylindrically extruded contact surfaces 37 and 38, a base portion 39 and a pair of studs 40 which are brazed or welded to base portion 39. Each stud 40 extends through panel q 39 and is insulated therefrom by means of insulating spacers 41 and 42 and an insulating bushing 43 which extends slightly past the surfaces 44 and 45 of panel 39. Contact member 32 is secured to panel 30 by washer 46, a nut 47 and a lock nut 48. Similar means may be used for attaching conductor 49 to stud 40 of contact member 32. Suitable passages 50 are provided on the bottom surface of member 32 to provide for the escape of any moisture which is contained in the insulating bushing 43 in the event the dial switch assembly is to be vacuum dried. Each of the contacting surfaces 37 and 38 contains a contact line 54. Contact member 32 is disposed so that contact lines 54 thereof are normal to lines extending radially outward from the axis of shaft 31.

Any two adjacent stationary contacts of the switch assembly are adapted to be interconnected through each of the two movable contact members 34 and 35. Both of the movable contact members are identical so only one will be described. As shown in Fig. 3 movable contact member 34 defines a pair of cylindrically shaped contacting surfaces 62, 63, each of which is similar to the contacting surface 16 of contact member 12 in Fig. l. Contact surfaces 62 and 63 are circumferentially spaced apart a distance corresponding to the circumferential spacing of the stationary contacts 32. Each of the coat ting surfaces 62 and 63 contain a contact line 64 when in this instance is positioned radially with respect to the axis of shaft 31.

Contact members 34 and 35 are biased towards each other and each movable member is adapted to engage two adjacent stationary contact members 32 by means of a pair of cantilever springs 66 and 67. In the illustrated embodiment the outer ends 68 of the springs are secured to contact member 34 by means of rivets and the other ends 69 extend radially inward toward the axis of rotation of shaft 31. These ends 69 are attached to a hub member 70 which is attached to shaft 31 by means of a pin 71. Hub member 70 functions to translate the rotational movement of shaft 31 to the movable contact members 34 and 35. In order to reduce the torque required of shaft 31 in switching from one contact position to another, each of the stationary contact members is provided with beveled or rounded edges 72.

If desired shaft 31 may be provided with an extension 7 73 which is attached to shaft 31 by means of a suitable universal coupling to allow turning the shaft from various positions either manually or by suitable motor means.

It will be apparent to those familiar with the transformer art that the illustrated dial switch is readily adaptable for use in a transformer as a no load tap changer. When so used the dial switch has many advantages over no load tap changers suggested in the prior art. It is well known that current carrying fiexiblc members are undesirable because the endurance of materials which are good conductors of electricity is less than that of carbon steel springs.

In addition flexible spring members which carry current tend to become annealed by the heating effect of the current overloads therein and thus eventually lose their ability to flex. Since members 34 and 35 carry practically all the current between contact members 32, spring members 66 and 67 may be manufactured from carbon spring steel rather than a copper alloy, allowing greater contact pressure to be maintained throughout the life of the switch.

In addition, it has been found that spring members 66 and 67 when made from carbon steel may be used as the only means for biasing contact members 34 and 35 towards contact member 32, thus eliminating any additional biasing means disposed between movable members 34 and 35 w ich might tend to cause these members to function improperly.

While the preferred embodiment of the present invention illustrates the movable contact members and the stationary contact members arranged so that during a switching operation their respective contact lines intersect to define an angle which changes from an acute angle to an obtuse angle, causing the point of contact to first move radially inward and then radially outward, it should be understood that other arrangements may be used with satisfactory results as long as the two contact lines intersect at one point and one member moves in an arc with respect to the other member.

It will also be apparent to those skilled in the art that contact members embodying the present invention may be readily adaptable for use in switches other than a dial switch employed as a no load tap changer without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A switch assembly comprising first and second contact members, said first contact member defining a curved contacting surface containing a first contact line disposed in a plane tangent to said surface, said second contact member defining a contacting surface containing a second Contact line disposed in said plane, said contacting surfaces being disposed with said first and second contact lines intersecting causing said contacting surfaces to be in contact at only one point, means for biasing one of said contact members toward the other member to maintain said point contact when said contact members are moved relative to each other parallel to said plane, and means for moving one of said contact members on an arc in said plane to cause said one point of contact to move simultaneously along said contact lines on said surfaces.

2. A switch assembly comprising first and second contact members, said first contact member defining a first cylindrically shaped contacting surface containing a first contact line disposed parallel to the axis of said first cylindrically shaped surface, said second contact member defining a second cylindrically shaped contacting surface containing a second contact line disposed parallel to the axis of said second cylindrically shaped surface, said contacting surfaces being disposed with said first and second contact lines intersecting causing said contacting surfaces to be in contact at only one point, means for biasing one of said contact members toward the other member to maintain said point contact when said members are moved relative to each other in a plane defined by said first and second contact lines, and means for moving one of said contact members on an arc in said plane to cause said one point of contact to move simultaneously along said contact lines on said surfaces.

3. A switch assembly comprising a stationary contact member defining a first cylindrically shaped contacting surface containing a first contact line disposed parallel to the axis of said first cylindrically shaped surface, a movable contact member defining a second cylindrically shaped contacting surface containing a second contact line disposed parallel to the axis of said second cylindrically shaped surface, said contacting surfaces being disposed with said first and second contact lines intersecting causing said contacting surfaces to be in contact at substantially only one point, means for biasing said movable contact members towards said stationary contact member to maintain said point contact when said members are moved relative to each other in a plane defined by said first and second contact lines, and means for rotating said movable contact member on an arc in said plane to cause said one point of contact to move simultaneously along said contact lines on said surfaces.

4. A dial switch assembly comprising a panel, a shaft adapted to be rotated on its axis normal to said panel, a plurality of stationary contact members fixedly attached tosaid panel and spaced circumferentially on the arc of a circle having its center on said axis of said shaft, each said stationary member defining a first cylindrically shaped contact surface containing a first contact line disposed parallel to the axis of said first surface and normal to a radial line extending from the axis of said shaft, a second contact member adapted to be moved from one stationary member to the next defining a second cylindrically shaped contacting surface containing a second contact line disposed parallel to the axis of said second surface, said second member being positioned to cause said first and second contact lines to intersect, means for biasing said second member toward said stationary members to cause said first and second contacting surfaces to be in engagement at substantially only one point defined by the intersection of said first and second contact lines, means for rotating said shaft, and means for translating the rotational movement of said shaft to said movable member to cause said one point of engagement to move simul taneously along said contact lines.

5. A dial switch assembly comprising a panel, a shaft adapted to be rotated on its axis normal to said panel, a plurality of stationary members fixedly attached to said panel and spaced equally on an arc of a circle having its center on the axis of said shaft, each said stationary member defining a pair of first contact surfaces disposed on opposite sides of a plane parallel to said panel, a pair of movable members each defining a pair of second contact surfaces, said second contact surfaces spaced apart a distance corresponding to the circumferential spacing of said stationary members, each of said contacting surfaces defining a portion of a right cylinder and containing a contact line parallel to the axis of said cylinder, said contact lines of said first surfaces being disposed normal to a radial line extending from said shaft, said contact lines of said second surfaces being disposed radially with respect to said axis of said shaft, said movable members being disposed to cause each said second contact line to intersect a different one of said first contact lines at substantially only one point, means for biasing each said movable member toward said stationary members to maintain said point contact between said surfaces and cause a wiping action between said surfaces when said movable members move, means for moving said movable members on an arc to cause each said one point of contact to move simultaneously along said intersecting contact lines, said moving means including said shaft and means connecting said movable member to said shaft.

6. A dial switch assembly comprising a panel, a shaft adapted to be rotated on its axis normal to said panel, a plurality of stationary members fixedly attached to said panel and spaced equally on an arc of a circle having its center on the axis of said shaft, each said stationary member defining a pair of first contact surfaces disposed on opposite sides of a plane parallel to said panel, a pair of movable members each defining a pair of second contact surfaces, said second contact surfaces spaced apart a distance corresponding to the circumferential spacing of said stationary members, each of said contacting surfaces defining a portion of a right cylinder and containing a contact line parallel to the axis of said cylinder, said contact lines of said first surfaces being disposed normal to radial lines extending from said axis of said shaft, said contact lines of said second surfaces being disposed radially with respect to said axis of said shaft, said movable members being disposed to cause each said second contact line to intersect a different one of said first contact lines at substantially only one point, a pair of cantilever springs serving as the only means for biasing each said movable member toward said stationary members to maintain said point contact between said surfaces and cause a wiping action between said surfaces when said movable members move, means for moving said movable members on an arc to cause each said one point of contact to move simultaneously along said intersecting contact lines, said moving means including said shaft, said cantilever springs and means connecting said springs to said shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,893,370 Jaros et al. Jan. 3, 1933 1,907,932 Pugh May 9, 1933 2,206,655 Allison et al. July 2, 1940 2,233,336 Bentley Feb. 25, 1941 FOREIGN PATENTS 511,855 France Oct. 1, 1920 

